How to use _.where() in underscore to compare values regardless of case

Question

I have a webpage where if something typed in search box it then iterates through a file for that value. I need it so that search/find not case sensitive. The case sensitivity must remain in the file but for comparison purposes it disregards the case.

So currently I am using underscore command:

arr=_.where(arr,filter);

but the 2 arrays arr and filter - I need them to be compared/used regardless of case so the end result arr contains results which will mixture of upper and lower case but matches value(s) in arr.

Answer 1

Try using filter instead:

var filter = ["Apple", "bANAna", "orange"];
var arr = ["apPle", "ORANGE"];

// make filter lower case once    
var filterLower = _.invoke(filter, "toLowerCase");

var arr2 = _.filter(arr, function(v) {
    // make entry lower case and see if it is in filterLower
    return _.contains(filterLower, v.toLowerCase());
});

console.dir(arr2);

<script src="http://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.4.4/underscore-min.js"></script>

Answer 2

Unfortunately, JS is not great when it comes to internationalized case-insensitive string comparison. If you're just sticking to ASCII though, the solution is fairly straightforward (using filter though, not where):

function getMatches(query, arr) {
  var lowerQuery = query.toLowerCase();
  return _.filter(arr, function(term) {
    return term.toLowerCase() == lowerQuery;
  });
}

Or if you want to precompute everything because you expect to make a lot of queries in the same JS session:

var index = _.groupBy(arr, function(term) { return term.toLowerCase(); });

// Post-process index to reduce memory footprint by turning redundant values to nulls
// (which take up less memory than arrays with a string in them).
index = _.object(_.map(index, function(terms, key) {
  return [key, (terms.length == 1 && terms[0].toLowerCase() == terms[0] ? null : terms)];
}));

function getMatches(query) {
  var lowerQuery = query.toLowerCase();
  return (lowerQuery in index ? index[lowerQuery] || lowerQuery : []);
}

This second method has the advantage of only computing toLowercase() the minimal number of times and minimal data storage because of the post-processing step.

Here's a JSFiddle for both